JP7574099B2 - Electrophotographic belt and electrophotographic image forming apparatus - Google Patents

Description

This disclosure relates to an electrophotographic belt and an electrophotographic image forming apparatus equipped with the electrophotographic belt.

Patent Document 1 discloses a conductive belt that is highly conductive and exhibits little change in electrical resistance even with long-term use. The conductive belt contains a hydrophobic fluorinated sulfonimide structure or an ionic liquid having hexafluorophosphate as an anion in a thermoplastic resin such as polyester.

JP 2015-230456 A

According to the inventors' investigations, when the electrophotographic belt according to Patent Document 1 was used as an intermediate transfer belt to form electrophotographic images over a long period of time, then left for a predetermined period of time, and then used again to form electrophotographic images, image defects due to poor toner transfer were observed.

One aspect of the present disclosure is directed to providing an electrophotographic belt that is resistant to exudation of cationic components to the surface even after long-term use in image formation and subsequent long-term storage, and that contributes to the stable formation of high-quality electrophotographic images. Another aspect of the present disclosure is directed to providing an electrophotographic image forming apparatus that can stably form high-quality electrophotographic images.

According to one aspect of the present disclosure, there is provided an electrophotographic belt having a layer containing a thermoplastic resin composition including a thermally melted mixture of a thermoplastic polyester resin, a cation having a hydroxyl group, an anion, and a compound having at least two amide groups in one molecule.
According to another aspect of the present disclosure, there is provided an electrophotographic image forming apparatus including the above-mentioned electrophotographic belt as an intermediate transfer belt.

According to one aspect of the present disclosure, it is possible to provide an electrophotographic belt whose belt surface condition is unlikely to change from its initial state even after long-term storage following repeated image output over a long period of time. Also, according to another aspect of the present disclosure, it is possible to provide an electrophotographic image forming apparatus capable of stably forming high-quality electrophotographic images.

1 is a schematic cross-sectional view showing an example of a full-color electrophotographic image forming apparatus utilizing an electrophotographic process. FIG. 2 is a schematic cross-sectional view of an injection molding device used in the examples. FIG. 2 is a schematic cross-sectional view of a primary blow molding device used in the examples. FIG. 2 is a schematic cross-sectional view of a secondary blow molding device used in the examples. 3 is an explanatory diagram of the mechanism by which the effect of the electrophotographic belt according to the present disclosure is exerted. FIG. 1 is an explanatory diagram of a configuration example of an electrophotographic belt according to the present disclosure.

The present inventors have conducted a study on image defects that occur when the electrophotographic belt according to the above-mentioned Patent Document 1 is used as an intermediate transfer belt for forming an electrophotographic image.
Specifically, the toner bearing surface of the electrophotographic belt was observed at a location corresponding to the image defect. As a result, untransferred toner and sticky deposits were confirmed. Furthermore, elemental analysis of the deposits confirmed that they were cationic components of the ionic liquid contained in the electrophotographic belt. From this, the present inventors recognized that in order to more stably form high-quality electrophotographic images, it is necessary to develop a technology for further suppressing the bleeding of cationic components in an electrophotographic belt made conductive with an ionic liquid.

The reason why the cationic components bleed onto the belt surface after the electrophotographic belt according to Patent Document 1 is subjected to repeated image output for a longer period of time than in the past and then stored for a long period of time is presumed to be as follows.
That is, the polyester resin contained in the thermoplastic resin composition is not completely compatible with the cations and anions, and microscopically, the polyester resin phase and the cation and anion phase are mixed together. Therefore, one of the cations and anions moves toward one surface of the belt, and the other moves toward the other surface (reverse side) of the belt according to the voltage application direction.
In the process of forming an electrophotographic image, there are a primary transfer in which the toner on the photosensitive drum is transferred to the electrophotographic belt, and a secondary transfer in which the toner on the electrophotographic belt is transferred to a transfer medium. The application direction of the voltage applied to the electrophotographic belt is opposite to that of the primary transfer and the secondary transfer with respect to the thickness direction of the electrophotographic belt.
Since the amount of current due to the voltage applied in the opposite direction during primary transfer and secondary transfer is usually different, the movement of cations and anions in the thickness direction tends to be biased in one direction. Therefore, by repeatedly outputting images for a longer period of time than before, the cations and anions become biased closer to the belt surface.
If the electrophotographic belt is stored for a long period of time under such conditions, a force acts on the cationic components to move toward the outer surface of the electrophotographic belt in an attempt to reduce the difference in interfacial energy between the outer surface of the electrophotographic belt and the atmosphere, and the cationic components bleed onto the outer surface of the electrophotographic belt.

The present inventors have conducted extensive research to suppress such bleeding of cations, and have found that an electrophotographic belt having a layer containing a thermoplastic resin composition including a thermally melted mixture of a thermoplastic polyester resin (hereinafter also simply referred to as "polyester resin"), a cation having a hydroxyl group, an anion, and a compound having at least two amide groups in one molecule can more effectively suppress bleeding of cationic components to the outer surface.
A hypothetical mechanism by which the exudation of cationic components can be better suppressed by the electrophotographic belt having the above-mentioned configuration will be described with reference to Fig. 5. Note that the cation 501 having a hydroxyl group, polyethylene naphthalate 502 as a polyester resin, and ethylene bisstearic acid amide 503 as a compound having at least two amide groups in one molecule shown in Fig. 5 are merely examples, and the present disclosure is not limited to these compounds in any way.
The cation 501 having a hydroxyl group and the polyester resin 502 have a high affinity because the hydroxyl group 501-1 and the ester bond 502-1 of the polyester resin 502 interact with each other by hydrogen bonding or ester exchange reaction (see arrow A in FIG. 5). In addition, the cation 501 having a hydroxyl group and the compound having at least two amide groups in one molecule (hereinafter, sometimes simply referred to as an "amide compound") 503 show a high affinity because the hydroxyl group 501-1 and the amide group 503-1 interact with each other (see arrow B in FIG. 5). Furthermore, the amide compound 503 and the polyester resin 502 show a high affinity because the amide group 503-1 and the ester bond 502-1 of the polyester resin interact with each other (see arrow C in FIG. 5). In this way, it is considered that the amide compound 503 mediates further improvement of the affinity between the cationic component 501 having a hydroxyl group and the polyester resin 502. In addition, the arrows A, B, and C in Fig. 5 are schematic representations of one mode of interactions between the hydroxyl group, the ester bond, and the amide group, respectively, and it is believed that in reality, these functional groups and bonds interact with each other in a complex manner. In addition, in Fig. 5, n, p, and q each independently represent an integer of 1 or more, and _R1 and _R2 each independently represent a hydrogen atom or an organic group.

Furthermore, as shown in FIG. 5, when the cation has two or more hydroxyl groups, the interaction with the polyester resin and the amide compound is enhanced, and thus bleeding of the cation onto the outer surface of the electrophotographic belt can be further suppressed.
Furthermore, even if the first layer contains polyetheresteramide (PEEA), since PEEA contains an ester bond and an amide group in the molecule, the bleeding of PEEA onto the outer surface of the electrophotographic belt can be suppressed by the same mechanism as above. Note that PEEA functions as a polymeric ionic conductive agent, and is therefore a preferred material for achieving even higher conductivity of the first layer of the electrophotographic belt.

The electrophotographic belt according to one embodiment of the present disclosure has a layer containing a thermoplastic resin composition including a thermally melted mixture containing a thermoplastic polyester resin, a cation having a hydroxyl group, an anion, and a compound having at least two amide groups in one molecule. In this specification, a compound having a cation and a pair of anions is sometimes referred to as an "ionic compound."

<Thermoplastic resin composition>
The thermoplastic resin composition according to the present disclosure is prepared by hot melt kneading a component including a thermoplastic polyester resin, a cation having a hydroxyl group, an anion, and a compound having at least two amide groups in one molecule. The heat-melt kneaded product includes a heat-melt kneaded product that can be obtained. PEEA may be heat-melted and kneaded together with these components.
The term "thermoplastic resin composition" refers to the process of kneading the resin in a molten state by heating the resin. In order to mix resins having different melting points well, the resins can be mixed at a temperature equal to or higher than the highest melting point of the resin. The mixing method is not particularly limited, and the mixing method may be performed using a single screw extruder, a twin screw extruder, a Banbury mixer, a roll mixer, or a combination of a single screw extruder, a twin screw extruder, a roll mixer ... A Brabender, a Plastograph, a kneader, or the like can be used.

<Thermoplastic polyester resin>
The thermoplastic polyester resin can be obtained by polycondensation of a dicarboxylic acid and a diol, polycondensation of an oxycarboxylic acid or a lactone, or polycondensation of a plurality of these components. A further polyfunctional monomer may be used in combination. The thermoplastic polyester resin may be a homopolyester containing one type of ester bond, or a copolyester (copolymer) containing a plurality of ester bonds.
As a suitable example of the thermoplastic polyester resin, at least one selected from the group consisting of polyalkylene terephthalate and polyalkylene naphthalate, which have high crystallinity and excellent heat resistance, can be mentioned. Also, as a copolyester (copolymer), a copolymer of polyalkylene terephthalate or polyalkylene naphthalate and polyalkylene isophthalate can be preferably used.
The copolymer in this case may be in the form of a block copolymer or a random copolymer.
From the viewpoint of high crystallinity and heat resistance, the number of carbon atoms of the alkylene in the polyalkylene terephthalate, polyalkylene naphthalate, and polyalkylene isophthalate is preferably 2 to 16. More specifically, the thermoplastic polyester resin is preferably polyethylene terephthalate, polyethylene naphthalate, or a copolymer of polyethylene terephthalate and polyethylene isophthalate.

The intrinsic viscosity of the thermoplastic polyester resin is preferably 1.4 dl/g or less, more preferably 0.3 dl/g or more and 1.2 dl/g or less. Thermoplastic polyester resins with an intrinsic viscosity of 1.4 dl/g or less have excellent fluidity during hot melt kneading. An intrinsic viscosity of 0.3 dl/g or more can more easily improve the strength and durability of electrophotographic belts. The intrinsic viscosity of the thermoplastic polyester resin is a value measured using o-chlorophenol as a diluting solvent for the thermoplastic polyester resin, with the concentration of the o-chlorophenol solution of the thermoplastic polyester resin at 0.5% by mass and the temperature at 25°C.

The content of the thermoplastic polyester resin in the thermoplastic resin composition is preferably 50% by mass or more, more preferably 60% by mass or more, and even more preferably 70% by mass or more, based on the total mass of the thermoplastic resin composition. By making the content of the thermoplastic polyester resin 50% by mass or more based on the total mass of the thermoplastic resin composition, it is easy to increase the mechanical strength of the thermoplastic resin composition.

<Cation having a hydroxyl group>
The cation having a hydroxyl group is not particularly limited, and examples thereof include ammonium ions, imidazolium ions, pyridinium ions, piperidinium ions, pyrrolidinium ions, and phosphonium ions. Among these, ammonium ions and imidazolium ions are preferred from the viewpoint of cost, etc.
Specific examples of the above cations include 2-hydroxyethylammonium ion, 2-hydroxypropylammonium ion, 2-hydroxyethyl-trimethylammonium ion, 2-hydroxypropyl-trimethylammonium ion, 2-hydroxy-3-methacryloyloxypropyltrimethylammonium ion, N-oleyl-N,N-di(2-hydroxyethyl)-N-methylammonium ion, etc. The above cations may be used alone or in combination of two or more kinds.
The amount of cation contained in the electrophotographic belt, together with the amount of the anion pair (as the amount of ionic compound), is preferably 0.5% by mass or more with respect to the total amount of the thermoplastic resin composition from the viewpoint of the electrical resistance of the electrophotographic belt. The upper limit is not particularly limited, but even if it is added in excess of 8% by mass, the effect of reducing electrical resistance is limited. In addition, from the viewpoint of good moldability of the thermoplastic resin composition, it is preferably 8% by mass or less. In addition, it can be blended into the thermoplastic resin composition as an ionic compound.

<Anion>
_The ^anion _{is not particularly} ^limited as long as it can form an ionic compound in a pair with the above cation, and examples of the anion ^include _ClO4- ^, Br- ^, _Cl- ^{, AlCl4-} , _Al2Cl7- , _{NO3- , BF4- , PF6- ,} ^{CH3COO- ,} _CF3COO- ^, _CF3SO3- ^{, (} _{CF3SO2 ) 3C-} ^, _AsF6- ^, _{SbF6- , F} ⁽ _HF ^{) n- ,} _{CH3CH2OSO3- , H2PO4- , CF3CF2CF2CF2SO3-} ^, _{CF3CF2CF2COO-} and anions represented by the following structural formula (1): Among these, sulfonimide-based anions represented by the following structural formula (1) are preferred from the viewpoints of affinity with polyester resins, electrical conductivity, etc.

Specific examples of anions satisfying structural formula (1) include bis(trifluoromethanesulfonyl)imide ion, bis(perfluoroethanesulfonyl)imide ion, bis(perfluoropropanesulfonyl)imide ion, bis(nonafluorobutanesulfonyl)imide ion (bis(perfluorobutanesulfonyl)imide ion), trifluoromethanesulfonylperfluoropropanesulfonylimide ion, trifluoromethanesulfonylperfluorobutanesulfonylimide ion, etc. The above anions may be used alone or in combination of two or more kinds.

<Compound Having at Least Two Amide Groups in One Molecule (Amide Compound)>
The compound having at least two amide groups in one molecule preferably has a molecular weight of 1000 or less, particularly 800 or less. The lower limit of the molecular weight of the amide compound is not particularly limited, but is preferably 200 or more. It is considered that the molecular weight of the amide compound within the above range allows the thermoplastic polyester, the ionic liquid, and the amide compound to interact more efficiently when they are thermally melted and kneaded.
In addition, the amide compound is preferably melted at the temperature during hot melt kneading. The melting point is preferably 70°C or more and less than 200°C, more preferably 100°C or more and 170°C or less. When the melting point is within the above range, the amide compound has excellent dispersibility and distribution in the thermoplastic resin composition during hot melt kneading, is easily arranged between the polyester resin and the cation and anion molecules, and is less likely to decompose due to thermal deterioration. Therefore, it is easy to further enhance the bleeding suppression effect.
The compound having at least two amide groups is preferably a fatty acid bisamide, which contains a fatty acid group (preferably a long-chain fatty acid group) and an amide group in the molecule, has excellent compatibility with thermoplastic polyester resins, and is relatively stable thermally and chemically.
From the viewpoints of compatibility with thermoplastic polyester resins and thermal and chemical stability, the carbon number of the long-chain fatty acid group is preferably in the range of 7 to 23. In addition, as a compound having at least two amide groups, an aromatic bisamide containing a fatty acid group and an amide group in the molecule, with the amide groups bonded to each other via an aromatic hydrocarbon, can also be used.

As the fatty acid bisamide, for example, alkylene fatty acid bisamides such as ethylene bis fatty acid amide can be used. Specific examples include methylene bis stearic acid amide (Tm (melting point): 142°C), ethylene bis capric acid amide (Tm: 161°C), ethylene bis lauric acid amide (Tm: 157°C), ethylene bis stearic acid amide (Tm: 145°C), ethylene bis hydroxystearic acid amide (Tm: 145°C), ethylene bis behenic acid amide (Tm: 142°C), hexamethylene bis stearic acid amide (Tm: 140°C), hexam ... Examples include ethylene bishydroxystearamide (Tm: 135°C), N,N'-distearyl adipamide (Tm: 141°C), N,N'-distearyl sebacamide (Tm: 136°C), ethylene bisoleamide (Tm: 115°C), ethylene biserucamide (Tm: 120°C), hexamethylene bisoleamide (Tm: 110°C), N,N'-dioleyl adipamide (Tm: 118°C), and N,N'-dioleyl sebacamide (Tm: 113°C).

The content (mass) of the compound having at least two amide groups in one molecule is preferably 2% or more and 80% or less, more preferably 5% or more and 50% or less, based on the total amount of the cation and anion (mass of the ionic compound).
When the content is 2% or more, the number of amide groups that interact with the thermoplastic polyester resin and the cations and anions is large, which is preferable for further suppressing bleeding.When the content is 80% or less, the decrease in melt viscosity of the thermoplastic resin composition is suppressed, and the strength decrease of the electrophotographic belt is easily suppressed.In addition, the excessive decrease in the mobility of the cations and anions is suppressed, and the resistance of the electrophotographic belt is easily suppressed.

<Polyetheresteramide (PEEA)>
As the PEEA, for example, there can be mentioned a compound having as its main component a copolymer composed of polyamide block units, such as nylon 6, nylon 66, nylon 11, or nylon 12, and polyether ester units.
For example, copolymers derived from lactams (e.g., caprolactam, lauryllactam) or salts of aminocarboxylic acids, polyethylene glycol, and dicarboxylic acids can be mentioned. Specific examples of the dicarboxylic acids include terephthalic acid, isophthalic acid, adipic acid, azelaic acid, sebacic acid, undecanedioic acid, dodecanedioic acid, and the like. PEEA can be produced by known polymerization methods such as melt polymerization. Of course, PEEA is not limited to these. PEEA may also be a blend or alloy of two or more types. The compound having at least two amide groups in one molecule used in this disclosure is mainly a low molecular weight compound having a molecular weight of 1000 or less, while PEEA is a polymer compound having a molecular weight larger than that.

<Additives>
Other components may be added to the thermoplastic resin composition as long as the effects of the present disclosure are not impaired. Examples of other components include conductive polymer compounds, antioxidants, UV absorbers, organic pigments, inorganic pigments, pH adjusters, crosslinking agents, compatibilizers, release agents, crosslinking agents, coupling agents, lubricants, insulating fillers, conductive fillers, and the like. These additives may be used alone or in combination of two or more types. The amount of additive used may be appropriately set and is not particularly limited.

<Electrophotographic Belt>
Fig. 6(a) shows a perspective view of an electrophotographic belt 500 having an endless belt shape according to one embodiment of the present disclosure. An example of the layer structure is a monolayer structure in which the cross section taken along line A-A' in Fig. 6(a) is constituted only by a first layer 501 containing the thermoplastic resin composition, as shown in Fig. 6(b-1). In this case, an outer surface 500-1 of the first layer becomes a toner carrying surface (outer surface) of the electrophotographic belt.
As another example of the layer configuration, as shown in Fig. 6(b-2), the cross section taken along line A-A' has a laminated structure having a first layer 501 and a second layer 502 covering the outer peripheral surface of the first layer 501. When the second layer 502 is provided, an outer surface 500-1 of the second layer 502 becomes the toner carrying surface of the electrophotographic belt.
An example of the second layer is a layer having excellent abrasion resistance and containing a cured product of an active energy ray curable resin. Such a second layer can be provided, for example, by applying a composition containing an active energy ray curable resin such as a photocurable resin onto the outer peripheral surface of the first layer and curing the composition.
The effect of the present disclosure in an electrophotographic belt having such a laminated structure is that the exudation of cationic components to the interface between the first layer and the second layer is suppressed, thereby suppressing a decrease in adhesion between the first layer and the second layer.
A third layer (not shown) may be provided to cover the inner peripheral surface of the first layer. Examples of the third layer include a resin layer for reinforcing the first layer and a conductive layer for making the inner peripheral surface of the electrophotographic belt conductive.

The first layer having an endless belt shape can be produced, for example, by the following method.
i) A method in which a mixture of a thermoplastic polyester resin, an ionic conductive agent having a sulfonimide structure as an anion, and a compound having at least two amide groups in one molecule is melt-extruded into a cylindrical shape; ii) A method in which pellets of the thermoplastic resin composition are molded into an endless belt shape by a molding method such as injection molding, stretch blow molding, or inflation molding.
Among them, examples of the method i) include a downward extrusion type internally cooled mandrel method, which allows the inner diameter of the extruded tube to be controlled with high precision, and a vacuum sizing method.

The method for producing an electrophotographic belt by stretch blow molding in the above ii) comprises the following steps: a step of molding a preform of the thermoplastic resin composition; a step of heating the preform; a step of placing the heated preform in a die for molding an endless belt and then injecting gas into the die to perform stretch blow molding; and a step of cutting the stretched molded product obtained by the stretch blow molding to obtain an endless belt.
The thickness of the first layer is preferably 40 μm or more and 500 μm or less, and particularly preferably 50 μm or more and 100 μm or less.
In order to improve the appearance of the surface of the electrophotographic belt and to improve the releasability of toner, etc., the surface of the thermoplastic resin composition layer may be coated with a treatment agent or may be subjected to a surface treatment such as polishing treatment. In addition, an outermost layer may be provided on the surface of the thermoplastic resin composition layer by sputtering or the like.
The use of the electrophotographic belt is not particularly limited, but it is preferably used as an intermediate transfer belt for temporarily transferring and holding a toner image, a conveying transfer belt for conveying a recording material as a transfer material, etc. In particular, it can be preferably used as an intermediate transfer belt. In addition, when the electrophotographic belt is used as an intermediate transfer belt, it is preferable that the surface resistivity of the electrophotographic belt is 1×10 ³ Ω/□ or more and 1×10 ¹² Ω/□ or less. If the surface resistivity is 1×10 ³ Ω/□ or more, the resistance is prevented from decreasing, the transfer electric field can be easily obtained, and the occurrence of missing images and roughness can be effectively prevented. If the surface resistivity is 1×10 ¹² Ω/□ or less, the transfer voltage can be more effectively suppressed from increasing, and the size of the power source and the increase in cost can be effectively suppressed.

<Electrophotographic Image Forming Apparatus>
An example of an electrophotographic image forming apparatus using an electrophotographic belt according to one embodiment of the present disclosure as an intermediate transfer belt will be described below. As shown in Fig. 1, this electrophotographic image forming apparatus has a so-called tandem type configuration in which electrophotographic stations of multiple colors are arranged side by side in the rotation direction of the intermediate transfer belt. In the following description, the reference characters of the components of each color of yellow, magenta, cyan, and black are respectively given suffixes Y, M, C, and k, but the suffixes may be omitted for similar components.

In FIG. 1, around the photosensitive drums (photoconductors, image carriers) 1Y, 1M, 1C, and 1k, charging devices 2Y, 2M, 2C, and 2k, exposure devices 3Y, 3M, 3C, and 3k, developing devices 4Y, 4M, 4C, and 4k, and an intermediate transfer belt (intermediate transfer body) 6 are arranged. The photosensitive drum 1 is rotated and driven at a predetermined peripheral speed (process speed) in the direction of the arrow F. The charging device 2 charges the peripheral surface of the photosensitive drum 1 to a predetermined polarity and potential (primary charging). The laser beam scanner as the exposure device 3 outputs a laser beam that is on/off modulated in response to image information input from an external device such as an image scanner or computer (not shown), and scans and exposes the charged surface of the photosensitive drum 1. This scanning and exposure forms an electrostatic latent image on the surface of the photosensitive drum 1 in response to the target image information.
The developing devices 4Y, 4M, 4C, and 4k contain toner of each color component, yellow (Y), magenta (M), cyan (C), and black (k), respectively. The developing device 4 to be used is selected based on image information, and developer (toner) is developed on the surface of the photosensitive drum 1, and the electrostatic latent image is visualized as a toner image. In this embodiment, a reversal development method is used in which toner is attached to the exposed portion of the electrostatic latent image to develop it. Furthermore, the charging device, exposure device, and developing device constitute an electrophotographic image forming means.

The intermediate transfer belt 6 is an electrophotographic belt having an endless shape. The intermediate transfer belt 6 is stretched by a plurality of rollers 20, 21, and 22 so that the outer circumferential surface of the intermediate transfer belt 6 abuts against the surface of the photosensitive drum 1. In this embodiment, the roller 20 is a tension roller that controls the tension of the intermediate transfer belt 6 to be constant, the roller 22 is a drive roller for the intermediate transfer belt 6, and the roller 21 is an opposing roller for secondary transfer. The intermediate transfer belt 6 is rotated in the direction of the arrow G by the drive of the roller 22. The primary transfer rollers 5Y, 5M, 5C, and 5k are disposed at primary transfer positions facing the photosensitive drum 1 across the intermediate transfer belt 6.
The unfixed toner images of each color formed on the photosensitive drum 1 are electrostatically primarily transferred in sequence onto the intermediate transfer belt 6 by applying a primary transfer bias of a polarity opposite to the charge polarity of the toner to the primary transfer roller 5 by a constant voltage source or a constant current source (not shown). A full-color image is then obtained on the intermediate transfer belt 6, in which the unfixed toner images of the four colors are superimposed. The intermediate transfer belt 6 rotates while carrying the toner images thus transferred from the photosensitive drum 1. After each rotation of the photosensitive drum 1 after the primary transfer, the surface of the photosensitive drum 1 is cleaned of transfer residual toner by a cleaning device 11, and the image forming process is repeated.

At the secondary transfer position of the intermediate transfer belt 6 facing the conveyance path of the recording material 7 as a transfer medium, a secondary transfer roller (transfer section) 9 is arranged in pressure contact with the toner image carrying surface of the intermediate transfer belt 6. At the rear side of the intermediate transfer belt 6 at the secondary transfer position, an opposing roller 21 is arranged as an opposing electrode of the secondary transfer roller 9 and to which a bias is applied. When the toner image on the intermediate transfer belt 6 is transferred to the recording material 7, a bias of the same polarity as the toner is applied to the opposing roller 21 by a transfer bias application means 28, for example, −1000 to −3000 V, and a current of −10 to −50 μA flows. The transfer voltage at this time is detected by a transfer voltage detection means 29. At the downstream side of the secondary transfer position, a cleaning device (belt cleaner) 12 is provided to remove the toner remaining on the intermediate transfer belt 6 after the secondary transfer.
The recording material 7 passes through a conveying guide 8 and is conveyed in the direction of the arrow H, and is introduced into the secondary transfer position. The recording material 7 introduced into the secondary transfer position is sandwiched and conveyed at the secondary transfer position, and at that time, a constant voltage bias (transfer bias) controlled to a predetermined value is applied from a secondary transfer bias application means 28 to the opposing roller 21 of the secondary transfer roller 9. By applying a transfer bias of the same polarity as the toner to the opposing roller 21, the four-color full-color image (toner image) superimposed on the intermediate transfer belt 6 at the transfer position is transferred collectively to the recording material 7, and a full-color unfixed toner image is formed on the recording material. The recording material 7 to which the toner image has been transferred is introduced into a fixing device (not shown) and heated and fixed.

The electrophotographic belt and the electrophotographic image forming apparatus according to the present disclosure will be specifically described below with reference to examples and comparative examples. Note that the electrophotographic belt and the electrophotographic image forming apparatus according to the present disclosure are not limited to the configurations embodied in the examples.
First, materials shown in the following Tables 1 to 5 were prepared as materials (thermoplastic polyester resin, ionic compound having cation and anion, amide compound, polyether ester amide, silicone particles) used in manufacturing electrophotographic belts according to the examples and comparative examples.
The cations in ionic compounds 1 to 6 shown in Table 2 correspond to cations having a hydroxyl group, while the cation in ionic compound 7 does not correspond to such a cation having a hydroxyl group. Amide compounds 1 and 2 shown in Table 3 correspond to compounds having at least two amide groups in one molecule, while amide compound 3 does not correspond to such a compound.

Measurement and evaluation methods for characteristic values)
The following describes evaluation methods (1) to (4) for electrophotographic belts according to Examples and Comparative Examples. In the following evaluations, an A4 size paper having Ra (arithmetic mean roughness) of 4 and Rzjis (ten-point mean roughness) of 15, which had been left in an environment of 23° C. temperature and 45% relative humidity for one day, was used as a transfer medium for image formation.

(1) Surface Resistivity The surface resistivity of the electrophotographic belt was measured based on the method specified in Japanese Industrial Standards (JIS)-K6911 1995. As the measuring device, a high resistance meter (product name: Hiresta UP MCP-HT450 type) with a main electrode having an inner diameter of 50 mm, a guard ring electrode having an inner diameter of 53.2 mm, and a probe (product name: UR-100) with an outer diameter of 57.2 mm was used. The high resistance meter and the probe were manufactured by Mitsubishi Chemical Analytech Co., Ltd.
The electrophotographic belt thus produced was left for 12 hours in an environmental test room controlled at a temperature of 23° C. and a relative humidity of 50%. Thereafter, a voltage of 250 V was applied to the electrophotographic belt to be measured for 10 seconds under an environment of a temperature of 23° C. and a relative humidity of 50%, and the surface resistivity of the electrophotographic belt was measured at four points in the circumferential direction. The logarithm of the average value (ρs) of the obtained surface resistivity with a base of 10 was taken as logρs, which was used as an index of electrical resistance. The values shown in the column of "Surface Resistivity Value" in Tables 6 to 8 are the logρs values.

(2) Initial Toner Transfer Efficiency The prepared electrophotographic belt was mounted as an intermediate transfer belt in a drum cartridge of a full-color electrophotographic device (product name: LBP-5200, manufactured by Canon Inc.) Using this full-color electrophotographic device, cyan toner and magenta toner were superimposed on a transfer medium to form a purple solid image.
The toner transfer efficiency was calculated from the toner amount F (g) held on the electrophotographic belt surface by the primary transfer from the photosensitive drum and the residual toner amount S (g) remaining on the electrophotographic belt surface after the secondary transfer to the transfer medium. Specifically, it is expressed by the following formula [1].
Toner transfer efficiency (%) = (1 - S/F) x 100 [1]

(3) Toner Transfer Efficiency After Durability Test The toner transfer efficiency of the image formed on the 300,000th transfer medium was measured by the same method as in (2) above.

(4) Toner transfer efficiency of electrophotographic belt left for 10 days after durability test The electrophotographic belt subjected to the durability test in (3) above was stored in a full-color electrophotographic device for 10 days under conditions controlled at a temperature of 23° C. and a relative humidity of 50%, and then a purple solid image was formed on the transfer medium by overlapping cyan toner and magenta toner. The toner transfer efficiency of the image formed on the transfer medium was measured by the same method as in (2) above.

[Examples 1 to 10]
The materials were preblended in advance according to the composition shown in Table 6, and then the materials were melt-kneaded in a twin-screw extruder (product name: TEX44α, manufactured by Japan Steel Works, Ltd.) to prepare a pellet-shaped thermoplastic resin composition. The melt-kneading temperature was adjusted to be within the range of 270° C. or higher and 300° C. or lower, and the melt-kneading time was approximately 3 minutes.
The obtained thermoplastic resin composition in pellet form was dried for 6 hours at a temperature of 140° C. Next, the dried thermoplastic resin composition in pellet form was charged into hopper 48 of an injection molding apparatus (product name: SE180D, manufactured by Sumitomo Heavy Industries, Ltd.) having the configuration shown in FIG.
The cylinder temperature was set to 290° C., the mixture was melted in the screws 42 and 42A, and then injection molded into a metal mold (not shown) through the nozzle 41A to produce the preform 104 (see FIG. 3). The temperature of the injection mold at this time was 30° C.

Next, the preform 104 was placed in the heating device 107 of the primary blow molding device shown in FIG. 3 at a temperature of 500°C to soften it, and the preform 104 was heated to 500°C. Then, in the blow mold 108, the mold temperature of which was kept at room temperature, the preform was blown with the stretch rod 109 and the force of air (blow air injection part 110) at a preform temperature of 160°C, air pressure of 0.3 MPa, and stretch rod speed of 1000 mm/s to obtain a blown bottle 112.

Next, the obtained blow bottle 205 was set in a cylindrical nickel metal mold 201 produced by electroforming in the secondary blow molding device shown in Fig. 4, and an outer mold 203 was attached. An air pressure of 0.1 MPa was applied to the inside of the blow bottle 205, and the blow bottle 205 was transferred to the inner surface of the mold by adjusting the pressure so that air would not leak to the outside, and the cylindrical nickel metal mold 201 was heated uniformly at 190°C by a heater 202 for a total of 60 seconds while being rotated.
Thereafter, the nickel cylindrical mold was cooled to room temperature by blowing air against it, the pressure applied to the inside of the blown bottle was released, and a blown bottle with improved dimensions was obtained by annealing. An endless belt was obtained by cutting both ends of the blown bottle. This endless belt was used as an electrophotographic belt as it is. The thickness of the electrophotographic belt was 70 μm. The results of the above evaluations (1) to (4) of this electrophotographic belt are shown in Table 6.

[Examples 11 to 15]
An endless belt was obtained in the same manner as in Example 1, except that the composition was as shown in Table 7. With this endless belt as a base layer, an outermost layer made of an acrylic resin, which is an active energy ray curable resin, was provided as follows for the purpose of improving the adhesion with other contact members such as a photosensitive drum and a cleaning blade and the releasability of the toner.

The following materials were mixed to form the outermost acrylic resin layer.
Dipentaerythritol hexaacrylate 100 parts by mass (product name: Light Acrylate DPE-6A, manufactured by Kyoeisha Chemical Co., Ltd.)
Carbon black (Ketjen black) 15 parts by mass (product name: MHI Black #273, manufactured by Mikuni Color Co., Ltd.)
Photopolymerization initiator: 5 parts by mass (product name: Irgacure (registered trademark) 184, manufactured by BASF Japan Ltd.).

Then, this mixture was diluted with methyl ethyl ketone so that the resin solid content concentration was 6% by mass, and the mixture was stirred with a stirrer to obtain a uniform mixture for forming an acrylic resin outermost layer. This mixture was uniformly applied to the outer peripheral surface of the base layer by a spray method, dried at 60°C for 1 minute to remove the solvent, and then irradiated with ultraviolet light to cure. In this way, an electrophotographic belt was obtained in which an acrylic resin outermost layer having a thickness of 2 μm was formed on the outer peripheral surface of the base layer. Note that an ultraviolet ray irradiation device (product name: UE06/81-3, manufactured by iGraphics Co., Ltd.) was used as an ultraviolet ray source, and ultraviolet rays were irradiated until the accumulated light amount reached 1000 mJ/cm ² , thereby UV curing the acrylic resin outermost layer. The results of the evaluations (1) to (4) performed on the obtained electrophotographic belt are shown in Table 7.

As shown in Tables 6 and 7, in the evaluation of the toner transfer efficiency of electrophotographic belts for the material compositions of Examples 1 to 15, the toner transfer efficiency after being left for 10 days after the durability test was all 92% or higher, which was very good.

[Comparative Examples 1 to 7]
An electrophotographic belt was produced in the same manner as in Example 1 or Example 11, except that the material types and blending amounts were as shown in the following Table 8. The evaluation results are shown in Table 8.

In Comparative Examples 1, 2, and 3, a cation (ionic compound 7) not containing a hydroxyl group is contained. In Comparative Examples 1 and 4, an amide compound is not contained. In Comparative Examples 5, 6, and 7, a compound having one amide group is contained instead of a compound having at least two amide groups in one molecule. In Comparative Example 7, an outermost layer made of an acrylic resin is provided.
In all the comparative examples, the toner transfer efficiency after the durability test and after leaving for 10 days was reduced by 10% or more compared to the initial state and after the durability test. This result verifies that the affinity due to the interaction between the thermoplastic polyester resin and the cation is not improved and the effect of suppressing adhesion of the bleeding matter to the belt surface is not obtained except for the combination of the cation and the compound having an amide group specified in the present disclosure.

1 Photosensitive drum 2 Charging device 3 Exposure device 4 Developing device 5 Primary transfer roller 6 Intermediate transfer belt 7 Recording material 9 Secondary transfer roller 11 Cleaning device 12 Cleaning device (belt cleaner)
20 tension roller 21 opposing roller 22 driving roller 28 transfer bias applying means 29 transfer high voltage detecting means

Claims (18)

An electrophotographic belt characterized by having a first layer containing a thermoplastic resin composition including a thermally melted mixture of a thermoplastic polyester resin, a cation having a hydroxyl group, an anion, and an amide compound having at least two amide groups in one molecule. The electrophotographic belt according to claim 1, wherein the molecular weight of the amide compound is 1,000 or less. The electrophotographic belt according to claim 1 or 2, wherein the cation has two or more hydroxyl groups in one molecule. The electrophotographic belt according to any one of claims 1 to 3, wherein the cation is at least one cation selected from the group consisting of ammonium ions, imidazolium ions, pyridinium ions, piperidinium ions, pyrrolidinium ions, and phosphonium ions. 5. The electrophotographic belt according to claim 1, wherein the anion has a structure represented by the following structural formula (1):

The electrophotographic belt according to any one of claims 1 to 5, wherein the thermoplastic polyester resin contains at least one selected from polyalkylene terephthalate and polyalkylene naphthalate. The electrophotographic belt according to claim 6, wherein the polyalkylene terephthalate is polyethylene terephthalate. The electrophotographic belt according to claim 6, wherein the polyalkylene naphthalate is polyethylene naphthalate. The electrophotographic belt according to any one of claims 1 to 8, wherein the amide compound is a fatty acid bisamide. The electrophotographic belt according to claim 9, wherein the fatty acid bisamide is ethylene bis fatty acid amide. The electrophotographic belt according to claim 10, wherein the ethylene bis fatty acid amide is ethylene bis stearic acid amide or ethylene bis capric acid amide. The electrophotographic belt according to any one of claims 1 to 11, wherein the amount of the ionic compound having a cation and an anion is 0.5% by mass or more and 8% by mass or less with respect to the total amount of the thermoplastic resin composition. The electrophotographic belt according to any one of claims 1 to 12, wherein the mass of the compound having at least two amide groups in one molecule is 2% or more and 80% or less of the mass of the ionic compound having a cation and an anion. The electrophotographic belt according to any one of claims 1 to 13, wherein the thermoplastic resin composition further contains polyether ester amide. The electrophotographic belt according to any one of claims 1 to 14, further comprising a second layer containing a cured product of a composition containing an active energy ray-curable resin. The electrophotographic belt according to any one of claims 1 to 15, wherein the electrophotographic belt has an endless belt shape. the electrophotographic belt has an endless shape and further includes a second layer covering an outer peripheral surface of the first layer,
15. The electrophotographic belt according to claim 1, wherein the second layer comprises a cured product of a composition containing an active energy ray-curable resin. An electrophotographic image forming apparatus having an intermediate transfer belt,
18. An electrophotographic image forming apparatus, wherein the intermediate transfer belt is formed of the electrophotographic belt according to claim 1.

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